Style code block captions (#689)

* Give code block captions same permalink as other elems

* Style code block captions like table captions

* Revert "Give code block captions same permalink as other elems"

This reverts commit 4f7e6da.

Author: jessetan

sass/_theme_rst.sass

@@ -95,6 +95,13 @@
     font-size: 12px
     line-height: 1.4
 
+  .code-block-caption
+    font-style: italic
+    font-size: 85%
+    line-height: 1
+    padding: 1em 0
+    text-align: center
+
   @media print
     .codeblock, div[class^='highlight'], div[class^='highlight'] pre
       white-space: pre-wrap